The development of the cluster of insulin resistance, hyperinsulinemia, abdominal adiposity, dyslipidemia, increased adrenocortical and sympathetic activity, elevated proinflammatory cytokines, hypercoagulability, and endothelial dysfunction, known as the metabolic or insulin resistance syndrome, is associated with premature morbidity and mortality in the elderly, and can be viewed as a process of accelerated metabolic aging. The work of our research group indicates that recurrent sleep curtailment in healthy young adults is associated with reduced glucose tolerance, insulin resistance, elevated evening cortisol levels, and increased cardiac sympathetic activity. These findings are characteristic of human aging and suggest that chronic sleep loss may be linked to the development of key features of the metabolic syndrome, and lead to accelerated metabolic senescence. Repeated sleep restriction in young adults is also accompanied by a marked decrease in plasma leptin, which raises the possibility that chronic sleep loss results in a state of perceived energy deficit at the level of the central nervous system leading to excessive food intake, weight gain, and increased long-term risk of obesity. The increasing prevalence of obesity in the US, particularly apparent between the ages 20-40, represents a major health problem. Voluntary sleep curtailment to accommodate work, family, and social responsibilities has become a hallmark of modern society, and may be particularly deleterious in middle-aged adults exposed to the metabolic risks of increasing adiposity. Therefore, this proposal focuses on the pathophysiology of recurrent sleep curtailment as a previously unrecognized risk factor for continued weight gain and accelerated metabolic aging in healthy middle-aged adults with overt predisposition to future obesity. We will also test the hypothesis that sleep restriction can trigger excessive food intake and interfere with the use of dietary approaches for reduction of adiposity. These experiments will be the first to examine the effects of varying sleep duration on hunger, satiety, food intake, daily energy balance, body fat deposition, and key aspects of the syndrome of insulin resistance in middle-aged adults at higher risk for accelerated metabolic aging. The proposed studies will also allow the preliminary evaluation of sleep extension as a novel behavioral intervention to improve metabolic health in this rapidly growing population.